Liquid composition suitable for use as a corrosion inhibitor and a method for its preparation

ABSTRACT

A liquid composition comprising a high-capacity aqueous carrier in which (i) a metalloid compound selected from the group consisting of antimony and germanium compounds and (ii) morpholine or derivative thereof are dissolved in the presence of (iii) unsaturated alcohol and (iv) water-soluble organic acid having reducing capacity, wherein the total concentration of said four components is preferably not less than 5% relative to the total weight of the composition. The composition is useful as a corrosion inhibitor. Also provided is a process for preparing the composition.

This application is a Continuation-In-Part of the U.S. national phase ofInternational Application No. PCT/IL2007/000192, filed 12 Feb. 2007,which designated the U.S. and claims priority to IL Application No.173706, filed 13 Feb. 2006, IL Application No. 185236, filed 13 Aug.2007; IL Application No. 187047, filed 30 Oct. 2007, IL Application No.189119, filed 29 Jan. 2008, the entire contents of each of which arehereby incorporated by reference.

FIELD OF THE INVENTION

This invention is pertaining primarily to corrosion inhibitors,especially to corrosion inhibitors for concentrated salt solutions. Itis particularly useful for certain oil drilling and oil productionsystems, and for selected absorption refrigeration systems wherein zincbromide and mixtures of zinc bromide and other salt brines (such ascalcium bromide) are basic components, and when the protection ofmetallic surfaces at elevated temperatures is critical.

BACKGROUND OF THE INVENTION

Well-drilling fluids and especially completion, packer, and workoverfluids are preferred in the form of clear salt aqueous solutions alsocommonly referred to as “clear brines”. Those fluids are called inaccordance with the phases of the hydrocarbon extraction process inwhich they are employed: completion fluids are those used after the wellhas been drilled and prior to the initiation of production; packerfluids are utilized as fluids in the annulus of the production tubing;and workover fluids are used during remedial operations on the well. Ofthe multiple functions of the fluid used in the well, a crucial one isbalancing formation pressures to prevent uncontrolled influx ofunderground fluids, which may result in a blowout. When formationpressure is high, as in the deeper wells, use of zinc bromide isparticularly useful, due to its high density in concentrated solutions.While saturated brine density is 1.20 g/cm³ for NaCl solutions, 1.46 forCaCl₂, 1.50 for NaBr and 1.71 for CaBr₂, the density of ZnCl₂ brine atsaturation attains 2.14 and the density of ZnBr₂ is as high as 2.65g/cm³.

When in use, a technical problem associated with the use of heavy brinefluids is their high corrosiveness, especially toward carbon steels,which are widely used in the construction of hydrocarbon wells, andparticularly at the elevated temperatures typically encountered in deepwells.

Known corrosion inhibitors, such as film-forming amines, which have beenused with high-density brines described in U.S. Pat. No. 4,304,677 andU.S. Pat. No. 4,292,183 do not generally provide adequate protectionfrom corrosion at those higher temperatures associated with the deepwells in which high-density brines are normally employed.

British Patent No. 2,027,686, U.S. Pat. Nos. 4,536,302, 4,728,446,4,784,779 and 4,980,074 have disclosed use of sulfur compounds as themain inhibitor-formula component that has been typical of the recentknown technology. Although the sulfur compounds are efficient corrosioninhibitors, there is an increased risk of stress corrosion cracking.There have been a number of catastrophic stress corrosion failures inthe oil industry that have been attributed to sulfur containingcorrosion inhibitors. As a result, the industry is seeking effective,non-sulfur corrosion inhibiting formulas.

Some non-sulfur corrosion-inhibition formulas are already known, butthey fall short in respect to the effectiveness considered necessary inthe industry. Thus, U.S. Pat. No. 4,539,122 describes use of erythorbicacid salts in combination with a molybdate salt, ferrous gluconate, andsodium gluconate. At more than 25 mpy (mili inches per year), thecorrosion rate claimed for 18.5 pounds per gallon brines (2.20 g/cm³) at300 degrees Fahrenheit (F), is too high for the most demandingapplications. A somewhat similar inadequacy was noted with U.S. Pat. No.4,980,074, which describes use of soluble aliphatic or aromaticaldehydes reacted with primary amines, and claims a less thansatisfactory corrosion rate of 28 mils per year for a 19.5 pounds pergallon (2.34 g/cm³) brine at 250 degrees F. Only when supported byaddition of sulfur compounds was the corrosion rate lowered to a levelof 10-13 mpy with the aforementioned brine at 250 degrees F. U.S. Pat.No. 4,971,709 discloses use of some metallic powders as inhibitors forzinc containing brines. The main disadvantage of the method is the verylow solubility of those powders, which cause precipitation of particlesthat might plug or damage a producing formation. Also U.S. Pat. No.4,539,122, which proposes inhibiting heavy brines with arseniccontaining compositions, is handicapped by the accumulative toxicity ofarsenic compounds. WO 01/46552 claims use of heteropoly complex anionsof transitional metal elements but omits to disclose the actualcorrosion rates obtained in application simulations. EP 1038936discloses the use of ammonia or amines in an amount effective to raisethe pH as additives in inhibiting corrosion in brines; however, theseadditives can interfere with the stability of the brines. Formulascombining antimony with acetylenic alcohols have been proposed, forexample in U.S. Pat. Nos. 4,498,997 and 4,522,658, for inhibitingoxidative effects of acidic aqueous environment.

In absorption refrigeration where lithium bromide solution is thepreferred fluid, additions of zinc bromide improve the saturationconcentration and provide a desirable low vapor pressure at absorberhigh temperatures. However, such solutions are extremely corrosive andcannot be used in the absence of very efficient corrosion inhibitors.Known additives include molybdates, chromates and nitrates. Theseadditives lessen corrosion, albeit not to a satisfactory level, whensignificant amounts of zinc bromide are incorporated into the workingfluids.

It is, therefore, an object of the present invention to provide a newcorrosion inhibitor formulation for reducing corrosion induced by heavybrine fluids.

It is further, an object of the present invention to provide corrosioninhibition mixtures, which are compatible with different applications ofworking fluids, particularly at elevated temperatures.

It is further another object of the present invention to providecorrosion inhibiting mixtures which reduce corrosion rate to below 25mpy when comprised in heavy brine fluids.

Another object of the present invention is to provide corrosioninhibiting mixtures which do not cause stress cracking to the apparatusin which they are used.

Still another object of the present invention is to provide use ofcombinations of corrosion inhibiting compounds in the manufacture ofcorrosion inhibiting mixtures.

Still another object of the present invention is to provide concentratedaqueous salt solutions that are strongly inhibited to preventunacceptable levels of corrosion on the metallic apparatus in which theyare used.

Still another object of the present invention is to provide concentratedaqueous salt solutions in which corrosion of steel is stronglyinhibited.

Another object of the present invention is to provide strongly inhibitedformulas of concentrated aqueous salt solutions that would preventcatastrophic sulfide stress cracking to the metallic apparatus in whichthey are used.

Another object of the present invention is to provide a method to usesynergistic corrosion inhibitor formulations that would adapt the levelof corrosion protection to the heavy brine fluids.

These and other objects of the present invention shall become clear asthe description proceeds.

SUMMARY OF THE INVENTION

The invention provides an antimony-based corrosion inhibitor forreducing metal corrosion induced by salt solutions, comprising anantimony compound and at least two compounds selected from two of thefour following compound families: i. morpholine and morpholinederivatives; ii. acetylenic alcohols; iii. ascorbic acid derivatives;and iv. selenium compounds.

Said antimony compound may be selected from antimony trioxide, potassiumantimony tartrate, antimony tartrate, and antimony trihalides. Saidmorpholine derivative may comprise alkylmorpholine derivatives,alkylmorpholine oxides, or other compounds comprising morpholinylstructure in their molecule. Said acetylenic alcohols are preferablyselected from 2-propyne alcohol and substituted 2-propyne alcohols. In apreferred embodiment of the invention said acetylenic alcohol ispropargyl alcohol. In another preferred embodiment of the invention saidacetylenic alcohol is selected from 1-alkyl substituted or1,1-dialkylsubstituted 2-propyne alcohols, an example being2-methyl-3-butyn-2-ol. In still another preferred embodiment of theinvention said acetylenic alcohol is selected from 3-substituted2-propyne alcohols, examples being 3-alkyl substituted or3-hydroxylalkyl substituted 2-propyne alcohols. In other preferredembodiment said acetylenic alcohol is selected from O-substituted2-propyne alcohols. Said ascorbic acid derivatives may be selected,without being limited to them, from ascorbic acid isomers, esters, andsalts thereof. In a preferred embodiment of the invention, thederivatives of ascorbic acid are selected from ascorbic acid,isoascorbic acid, and salts thereof. Said selenium compound ispreferably selected from selenium oxide, selenium salts, such asselenium halides, and selenium oxychloride.

A corrosion inhibitor according to the invention is preferably used in asolution comprising a salt selected from zinc bromide, zinc chloride,calcium bromide, calcium chloride, and mixtures thereof. Said metal maybe selected from carbon steels and chromium-alloyed steels. An inhibitoraccording to the invention reduces the rate of corrosion, induced bysaid salt solution, to below 40 mpy, preferably to below 25 mpy, andstill more preferably to below 10 mpy. An inhibitor according to theinvention may reduce the rate of corrosion induced by said salt solutionto below 5 mpy. Said antimony compound is preferably selected fromantimony bromide and antimony chloride. In a preferred embodiment of theinvention, the anticorrosive inhibitor comprises an antimony compoundand two compounds selected from two different families of the above saidfour families. In a preferred embodiment of the invention, said twocompounds are selected from morpholine, propargyl alcohol, isoascorbicacid, ascorbic acid, and selenium dioxide. In a preferred embodiment ofthe invention a preferred inhibitor according to the invention maycomprise an antimony compound and a compound combination selected from:a) propargyl alcohol, morpholine; b) morpholine, isoascorbic acid; c)propargyl alcohol, isoascorbic acid; and d) propargyl alcohol, seleniumdioxide. An inhibitor according to the invention may comprise anantimony compound and three compounds selected from three differentfamilies of said four families. Said three compounds may comprise acombination selected from: a) propargyl alcohol, morpholine, seleniumdioxide; b) propargyl alcohol, morpholine, isoascorbic acid; and c)morpholine, isoascorbic acid, selenium dioxide. An inhibitor accordingto the invention may comprise an antimony compound and four compoundsselected from four different families of said four families. Said fourcompounds may be propargyl alcohol, morpholine, selenium dioxide, andisoascorbic acid.

The invention relates to an inhibitor composition, comprising anantimony compound and any combination of two or more compounds selectedfrom the following compound families: i. morpholine and morpholinederivatives; ii. acetylenic alcohols; iii. ascorbic acid derivatives;and iv. selenium compounds; wherein at least two compounds of saidcombination belong to different families. The inhibitor composition maycomprise two or more compounds belonging to the same family. Theantimony-based corrosion inhibitor according to the inventionessentially comprises a non-sulfur mixture. An antimony-based corrosioninhibitor or an antimony-based anticorrosive composition according tothe invention may comprise additional components that improve itsanticorrosive or other properties. Advantageously, the inhibitorcomposition may further comprise an amine. An inhibitor according to theinvention is preferably effective in inhibiting or reducing corrosionrate in salt solutions used in hydrocarbon drilling, in completionfluids, packer fluids, and workover fluids. In a preferred embodiment ofthe invention, the inhibitor is effective in inhibiting or reducingcorrosion rate in salt solutions used in absorption refrigerationsystems. In another preferred embodiment of the invention, the inhibitoris effective in inhibiting or reducing corrosion rate in heavy brinefluids at elevated temperatures.

The invention is directed to the use of a mixture comprising an antimonycompound and at least two compounds selected from at least two of thefour following compound families: i. morpholine and morpholinederivatives; ii. acetylenic alcohols; iii. ascorbic acid derivatives;and iv. selenium compounds; in preparing a corrosion inhibitor forreducing or inhibiting corrosion induced by salt solutions. In the useaccording to the invention, said mixture may, for example, comprise anantimony compound and two compounds selected from morpholine ormorpholine derivatives, and acetylenic alcohols, and may reduce thecorrosion rate induced by said salt solution to a value of about 40 orlower. Said two compounds may be selected from the followingcombinations: a) propargyl alcohol, morpholine; b) morpholine,isoascorbic acid; c) propargyl alcohol, isoascorbic acid; and d)propargyl alcohol, selenium dioxide; wherein the rate of corrosioninduced by said salt solution may be reduced according to the inventionto about 30 mpy or lower. In another preferred use according to theinvention, said mixture may comprise an antimony compound and threecompounds selected from morpholine or morpholine derivatives, acetylenicalcohols, ascorbic acid derivatives, and selenium compounds. Said threecompounds may be selected from morpholine or morpholine derivatives,acetylenic alcohols, ascorbic acid or isoascorbic acid or a saltthereof, and a selenium compound. Said three compounds may be selectedfrom the following combinations: a) propargyl alcohol, morpholine,selenium dioxide; b) propargyl alcohol, morpholine, isoascorbic acid;and c) morpholine, isoascorbic acid, selenium dioxide; wherein the rateof corrosion induced by a salt solution is reduced by using saidcorrosion inhibitor according to the invention to about 25 mpy or lower.In a preferred embodiment of the invention, the use of said mixturefurther comprises admixing an amine into said inhibitor mixture or intosaid brine. In the use of the invention the corrosion inhibitorcomprises an antimony compound and a compound combination selected from:a) propargyl alcohol, morpholine, selenium dioxide, isoascorbic acid;and b) propargyl alcohol, morpholine, selenium dioxide, hexamine;wherein the rate of corrosion induced by a salt solution is reduced bythe corrosion inhibitor used according to the invention to about 10 mpyor lower. In the use according to the invention, the corrosion inhibitoris essentially a non-sulfur inhibitor. In said use of the invention, thecorrosion inhibitor is introduced into a salt solution inducingcorrosion, said salt solution comprising, typically, salts selected fromzinc bromide, zinc chloride, calcium bromide, calcium chloride, andmixtures thereof. In said use, the corrosion inhibitor is effective ininhibiting or reducing the corrosion rate in salt solutions incorporatedin hydrocarbon drilling, completion, production and workover, and inabsorption refrigeration systems. Use of the invention comprises aneffective corrosion inhibition in salt solutions at elevatedtemperatures.

The invention further relates to a salt solution comprising a corrosioninhibitor as described above, wherein the corrosion induced by said saltsolution is essentially reduced by said corrosion inhibitor. A saltsolution according to the invention, having usually a density from about1.20 to about 2.65 g/cm³, preferably comprises zinc bromide, zincchloride, calcium bromide, calcium chloride, and mixtures thereof. Thesalt solution of the invention is usually incorporated in technologiesassociated with hydrocarbon drilling, completion, production andworkover, and absorption refrigeration systems. A salt solutionaccording to the invention is effective in inhibiting corrosion orreducing the rate of corrosion induced by heavy brine fluids at elevatedtemperatures. Said salt solution comprises a corrosion inhibitor whichis essentially a non-sulfur inhibitor. Said salt solution may furthercomprise an amine.

The invention provides a method of inhibiting metal corrosion in a heavybrine fluid, comprising admixing to said fluid an antimony compound, andtwo or more compounds selected from at least two of the four followingcompound families: i. morpholine and morpholine derivatives; ii.acetylenic alcohols; iii. ascorbic acid derivatives; and iv. seleniumcompounds; wherein said two or more selected compounds belong to atleast two of said four families. The invention is also directed to aformulation for use in inhibiting metal corrosion in heavy brine fluids,comprising an antimony compound, and at least two compounds selectedfrom at least two of the four following compound families: i. morpholineand morpholine derivatives; ii. acetylenic alcohols; iii. ascorbic acidderivatives; and iv. selenium compounds. The invention thus relates to amethod of inhibiting metal corrosion in concentrated aqueous saltsolutions, comprising adding, together with an antimony compound, atleast two other compounds, at relatively low concentrations, to thesolution, wherein said compounds belong to said compound families.Including an amine may be sometimes useful. Said salt solutions may, invarious situations, combine with, without being limited to them,lithium, sodium, potassium, calcium, zinc, chlorides, bromides,acetates, and formates, and more typically will comprise calcium or zincas cation, and chloride or bromide as anion. Said salt solutions, orheavy brine fluids, as they are in this context interchangeably calledin this application, will have densities usually from about 1.20 toabout 2.65 g/cm³. Said antimony compound is preferably an antimonyhalide, such as antimony chloride (SbCl₃) or antimony bromide (SbBr₃).Said morpholine derivative may, for example, comprise alkylmorpholinederivatives, said acetylenic alcohol may comprise, for example, propyneor butyne derivatives, said ascorbic acid derivative is preferably anisomer or a salt of ascorbic acid. Said selenium compound may comprise aselenium salt or oxide. Optionally includable amine may comprise, forexample, a tertiary amine such as hexamine.

The present invention is based on the discovery that mixtures containingan antimony compound together with various combinations of morpholinecompounds, antimony compounds, acetylenic alcohols, ascorbic acidderivatives, and selenium compounds, provide good corrosion protectionto metallic surfaces of apparatuses being in contact with brines andworking fluids, at relatively low concentrations. The corrosioninhibiting mixtures of the invention are particularly useful for heavybrine salts solutions containing zinc bromide and zinc chloride, andespecially when used at elevated temperatures. The corrosion protectionremains strong at those high temperatures that may be encountered inprocesses such as hydrocarbon drilling, completion, production andworkover, as well as in absorption refrigeration systems. The presentinvention is further especially based on the discovery that whencombined at the right ratios, said abovementioned compounds provide asynergistically enhanced protection to metal surfaces coming in contactwith a salt solution, in particular with a concentrated solutioncontaining zinc bromide that was properly modified by adding saidsynergistic mixtures.

As will be described in greater detail in the following, compoundsselected from among four compound families were co-introduced toconcentrated aqueous solutions together with antimony compounds to formcorrosion inhibiting mixtures of the present invention to be tested.Accordingly, varying corrosion inhibiting rates were obtained, dependingon the compounds selection, and on their concentrations. These testsenabled both setting the reduction in corrosion rate for each mixtureand diagnosing the synergistic effect taking place in the addition of acompound of a certain family compared to a reference mixture. As will bedemonstrated, the mixtures used for corrosion inhibition reducedsignificantly the rate of corrosion down to only several mpy in certaincases.

The invention relates to an anticorrosive mixture of compoundscontaining an antimony compound and at least two compounds selected fromthe following compound families: i) morpholine and morpholinederivatives; ii) acetylenic alcohols; iii) ascorbic acid derivatives;and iv) selenium compounds. Various effective corrosion inhibitioncombinations may be produced from the compounds belonging to saidfamilies, all being included within the spirit of the present invention.A combination of compounds within the scope of the invention maycomprise more than one compound of one family. A corrosion inhibitoraccording to the invention is preferably used in a brine comprising asalt selected from zinc bromide, zinc chloride, calcium bromide, calciumchloride, and mixtures thereof. Said protected metal may be selected,for example, from carbon steels, chromium-alloyed steels, and stainlesssteels of various types. The inhibitor of the invention reduces the rateof corrosion induced by said salt solution below 40 mpy, preferablybelow 25 mpy, and still more preferably below 10 mpy. Variouscombinations of the compounds according to the invention may provide invarious environments anticorrosive inhibition comprising values below 5mpy. Said antimony compound is preferably an antimony halide, such asantimony chloride or antimony bromide. Said morpholine derivative may,for example, comprise optionally substituted morpholine (for the sake ofbrevity, the term “morpholine derivative” may be used for “morpholine orits derivative”), said acetylenic alcohol may comprise, for example,propyne derivatives, such as 2-methyl-3-butyn-2-ol,4-methyl-1-pentyn-3-ol, 1-hexyn-3-ol, 4-ethyl-1-octyn-3-ol, propargylalcohol, alkoxylated propargyl alcohols, benzylbutynol,1-ethynylcyclohexanol, 5-decyne-4,7-diol, and mixtures thereof. Saidascorbic acid derivative is preferably an isomer or a salt of ascorbicacid. Optionally includable amine may comprise, for example, a tertiaryamine such as hexamine.

The invention provides a formulation to be added to brines to inhibitthe corrosion rate, which formulation may be a concentrated solution ora suspension of said compounds of the mentioned four families. Saidformulation may alternatively be a solid comprising said compounds.

It is understood that said compounds may be present in variousconsistencies in an effective mixture or formulation, and that they mayinteract or even react in the mixture to form adducts or salts orcomplexes or other products of such interactions; the words mixture andformulation are used interchangeably in that context.

In one preferred embodiment of the invention, the corrosion inhibitor ofthe invention comprises a combination of compounds selected fromantimony bromide, antimony chloride, morpholine, propargyl alcohol,isoascorbic acid, hexamine, and selenium dioxide. Said inhibitorcomprises at least three compounds selected from three differentcompound families. In a preferred embodiment, the inhibitor of theinvention comprises a combination selected from the group ofcompound-triplets consisting of antimony bromide, propargyl alcohol, andmorpholine; antimony bromide, morpholine, and isoascorbic acid; antimonybromide, propargyl alcohol, and isoascorbic acid; and antimony bromide,propargyl alcohol, and selenium dioxide. In other preferred embodimentof the invention, the anticorrosive inhibitor may comprise fourcompounds selected from the group of compound-quadruplets consisting ofantimony bromide, propargyl alcohol, morpholine, selenium dioxide;antimony bromide, propargyl alcohol, morpholine, isoascorbic acid; andantimony bromide, morpholine, isoascorbic acid, selenium dioxide. Aninhibitor according to the invention may comprise more than fourcompounds selected from antimony compounds and said four compoundfamilies. In a preferred embodiment of the invention, the inhibitor is acompound-quintuplet consisting of antimony bromide, propargyl alcohol,morpholine, selenium dioxide, and isoascorbic acid. In anotherembodiment, the inhibitor is a compound quintuplet consisting ofantimony bromide, propargyl alcohol, morpholine, selenium dioxide, andhexamine. It is understood that other combinations, possibly comprisingtwo or more materials belonging to the same family, may be useful invarious practical applications.

Preferred examples of mixtures comprising such corrosion inhibitingcombinations, will now be described in greater detail.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To more fully illustrate the present invention, several non-limitingexamples are subsequently presented. In determining the corrosion rateshown in the following examples, mild steel C-4130 corrosion couponswere rinsed in acetone, dried and weighed to the nearest 0.1 mg. One ortwo coupons were placed into a glass container containing 125 ml or 250ml of the test fluid to thereby provide a volume to surface area ratioof 20 ml per sq. in. or in 200 ml of the test fluid to thereby provide avolume to surface area ratio of 45.6 ml per sq. in. The glass containerholding the coupons and the test fluid was then placed into an agingcell and pressurized to 500 psi with an inert medium such as nitrogen.The cell was next placed in an oven at the desired temperature for therequired test period. When not indicated otherwise, the temperature was177° C. (350° F.) and the test duration was 7 days. After aging, thecoupons were removed from the cell, brushed and rinsed sequentially inhot water and acetone. They were later dried, re-weighed to the nearest0.1 mg and the weight-loss was calculated. For corrosion ratecalculations the formula given below was used:mpy=534W/DATwhere mpy=corrosion rate in mili inches per year

-   -   W=weight loss, mg    -   D=density of coupon, g/cm³    -   A=area of coupon, sq. in.    -   T=exposure (aging) time, hr

As mentioned above, antimony compounds and compounds of four familieswere used in preparing corrosion inhibiting mixtures, namely morpholineand morpholine derivatives, acetylenic alcohols, ascorbic acidderivatives such as isomers or salts, and selenium compounds, optionallyusing also amines. Without being limited to them, the followingcompounds may be included in the inhibiting mixtures: optionallysubstituted morpholine, antimony chloride, antimony bromide, antimonytrioxide, potassium antimony tartrate, antimony tartrate, propargylalcohol, 2-methyl-3-butyn-2-ol, 4-methyl-1-pentyn-3-ol, 1-hexyn-3-ol,4-ethyl-1-octyn-3-ol, propargyl alcohol, alkoxylated propargyl alcohols,benzylbutylol, 1-ethynylcyclohexanol, 5-decyne-4,7-diol, isoascorbicacid, ascorbic acid, hexamine, selenium dioxide, and selenium chloride.

Effective corrosion inhibiting compositions may be obtained by combiningdifferent compounds detailed above, particularly morpholine, antimonychloride or antimony bromide, propargyl alcohol, isoascorbic acid, andselenium dioxide, possibly with addition of an amine such as hexamine.

In one aspect of the present invention is provided a three componentcomposition for inhibiting corrosion in salt solutions. Particularexamples of such three components compositions are as follows:

-   A composition that contains SbBr₃, propargyl alcohol, and selenium    dioxide.-   A composition that contains morpholine, SbBr₃, and propargyl    alcohol.-   A composition that contains SbBr₃, propargyl alcohol, and    isoascorbic acid.

In still another aspect, the present invention provides a four componentcomposition for inhibiting corrosion in salt solutions. Particularexamples of such four components compositions are as follows:

-   A composition that contains morpholine, SbBr₃, propargyl alcohol,    and isoascorbic acid.-   A composition that contains morpholine, SbBr₃, propargyl alcohol,    and selenium dioxide.-   A composition that contains morpholine, SbBr₃, isoascorbic acid, and    selenium dioxide.

In still another aspect, the present invention provides a compositionfor inhibiting corrosion in salt solutions comprising more than fourcomponents. Particular examples of such compositions are as follows:

-   A composition that contains morpholine, SbBr₃, propargyl alcohol,    selenium dioxide, and hexamine.-   A composition that contains morpholine, SbBr₃, propargyl alcohol,    isoascorbic acid, and selenium dioxide.

From the viewpoint of corrosion inhibition, antimony bromide may usuallybe replaced by antimony chloride.

A suitable combination of at least three components selected fromantimony compounds and the four families according to the invention mayprovide the desired corrosion inhibitor for various practicalsituations, as a skilled person will appreciate.

In a preferred embodiment of the invention, a salt solution containingzinc bromide at 10 wt. % to 82 wt. %, preferably 30 wt. % to 78 wt. %,and/or calcium bromide at 1 wt. % to 56 wt. %, preferably 15 wt. % to 35wt. %, and/or calcium chloride at 0 wt. % to 20 wt. % is inhibited by acorrosion inhibitor comprising two or more compounds selected fromgroups i. to iv. defined above, wherein said salt solution preferablycontains less than 1 wt. % of said compounds, for example less than 0.8wt. %, preferably 0.5 wt % or less. Said compounds constituting theinhibitor may be present in the brine in amounts, e.g., from 50 ppm to0.5 wt. %. Said corrosion inhibitor preferably reduces the corrosionrate of steel, even at elevated temperatures, wherein said steel may befor example carbon steel, or chromium-alloyed steel, such as 13%chromium steel (Alloy 410).

In still another embodiment of the invention, a salt solution containingzinc bromide at 10 wt. % to 82 wt. %, preferably 30 wt. % to 78 wt. %,and/or calcium bromide at 1 wt. % to 56 wt. %, preferably 15 wt. % to 35wt. %, and/or calcium chloride at 0 wt. % to 20 wt. % is inhibited by acorrosion inhibitor comprising selenium dioxide, when in contact at 177°C. with carbon steel used in oilfield installation, wherein no more thanhalf a percent of each of said components selected from said fourfamilies is added in either solid form or dissolved in a suitableaqueous or organic solvent. It is for those skilled in the art to choosethe most effective inhibitor dosage for the particular salt solutioncomposition and the specific temperature of use. In a variation of theaforementioned embodiment, the anti-corrosion effect is synergisticallyaugmented by further addition of no more than 1 wt. %, preferably nomore than 0.4 wt. % of a 1:20 weight per weight (w/w) solution ofantimony chloride in propargyl alcohol. Here also, it is for thoseskilled in the art to choose the most effective inhibitor dosage for theparticular salt solution composition and the specific temperature ofuse.

Salt solutions that are corrosion inhibited may be prepared byintroducing and mixing the components in any order. For example, aprocess for the preparation of an inhibited brine may compriseintroducing a concentrated aqueous or non-aqueous solution of some ofthe inhibiting compounds into the brine, or the process may alsocomprise introducing solids or liquids into the brine. One or more ofthe inhibiting compounds may serve as a solubilizing or suspendingmedium for one or more other inhibiting compounds.

In one particular embodiment of the present invention the corrosioninhibited salt solutions may comprise any of zinc bromide, zincchloride, calcium bromide, calcium chloride and mixtures thereof, andany of the compositions detailed above.

The following Examples 1-7 demonstrate the synergistic effect observedin particular corrosion inhibiting mixtures introduced into zinc bromideand calcium bromide salt solutions and tested according to the abovedescribed procedure. The corrosion inhibiting components in thesemixtures are selected from morpholine, antimony chloride or antimonybromide, propargyl alcohol, isoascorbic acid, hexamine, and seleniumdioxide, and the mixtures tested, whether incorporating only part of thecomponents or all, were compared to a reference example where nocorrosion inhibiting compound is introduced.

The above-described procedure was employed with an 18.2 ppg (pounds pergallon) salt solution made of 44.3 wt. % zinc bromide and 25.8 wt. %calcium bromide. The coupons were of carbon steel C-4130, thetemperature 350° F., the pressure 500 psi and the duration of exposure168 hours.

The experiments which were designed to look for any Environment-AssistedCracking (EAC) used U-bend coupons that were prepared as recommended inASTM No. GM 58 from 309, 310 and 410 stainless steels and exposed for 1week at 350° F. to the cited synergistically inhibited 18.2 ppg saltsolution. No signs of cracking were observed on any of the mentionedcoupons after aging.

EXAMPLE 1 Reference Example

Corrosion inhibition was first tested for a blank salt solution. Thecorrosion rate was 46.2 mpy.

Three components selected from morpholine, antimony compound, andpropargyl alcohol were then tested separately. Table 1 herein shows thatuse of one component lowered the corrosion rate to 37-43 mpy. A smallamount of antimony chloride (100-200 ppm) and propargyl alcohol resultedin a small decrease in the corrosion rate to 41-45 mpy. A larger amountof antimony bromide (500 ppm) and propargyl alcohol resulted in a largerdecrease in the corrosion rate, to 30 mpy.

TABLE 1 Corrosion Rate Morpholine SbBr₃ SbCl₃ Propargyl Alcohol (mpy)(wt. %) (ppm) (ppm) (wt. %) 46.2 — — — — 42.5 0.25 — — — 37.0 — 2500 — —41.9 — — — 0.25 30.1 —  500 — 0.2 40.8 — — 100 0.2 45.3 — — 200 0.2

EXAMPLE 2 Three Components-Mixture

A three component mixture was tested for decrease in corrosion rate. Thecombination of morpholine+propargyl alcohol+isoascorbic acid had noeffect on the corrosion rate but other combinations of three componentsresulted in decreases in the corrosion rate. Using antimony compoundstogether with either morpholine and propargyl alcohol, propargyl alcoholand isoascorbic acid, or morpholine and isoascorbic acid, resulted insignificantly reduced corrosion rate values down to lower than 15 mpy,and in certain cases lower than 10 mpy, as can be appreciated from Table2 below.

TABLE 2 Corrosion Rate Morpholine SbBr₃ SbCl₃ Propargyl AlcoholIsoascorbic acid (mpy) (wt. %) (ppm) (ppm) (wt. %) (wt. %) 47.5 0.3 — —0.2 0.5 45.0 0.3 — — 0.2 0.5 26.8 0.3 — 100 0.2 — 27.5 0.3 — 100 0.2 —18.0 — — 100 0.2 0.5 31.7 — — 100 0.2 0.5 12.5 0.3 150 — — 0.4 11.0 0.3150 — — 0.5 8.1 0.3 150 — — 0.5 13.9 0.3 150 — — 0.5 15.5 0.3 150 — —0.5 10.9 0.3 150 — — 0.6 12.6 0.3 — 100 — 0.5 13.8 0.3 — 100 — 0.5 9.60.3 — 100 — 0.5 10.2 0.3 — 100 — 0.5

Based on the above results, the following conclusions regarding theabove different combinations were drawn:

-   a) morpholine+propargyl alcohol+isoascorbic acid had little effect    on the corrosion rate.-   b) morpholine+antimony chloride+propargyl alcohol decreased the    corrosion rate to 27-28 mpy.-   c) antimony chloride+propargyl alcohol+isoascorbic acid decreased    the corrosion rate to 18-32 mpy.-   d) morpholine+antimony bromide or antimony chloride+isoascorbic acid    decreased the corrosion rate to 8-16 mpy.

EXAMPLE 3 Four Components-Mixture

A four-component mixture, consisting of morpholine, antimony chloride,propargyl alcohol, and isoascorbic acid was tested and resulted in avery low corrosion rate (3-6 mpy).

TABLE 3 Propargyl Corrosion Rate Morpholine SbCl₃ Alcohol Isoascorbicacid (mpy) (wt. %) (ppm) (wt. %) (wt. %) 3.1 0.3 100 0.2 0.5 3.2 0.3 1000.2 0.5 5.5 0.3 100 0.2 0.5 5.2 0.3 100 0.2 0.5

EXAMPLE 4 Use of Selenium Dioxide

The positive effect of selenium dioxide was tested alone and in a threecomponent combination with antimony bromide and propargyl alcohol. Table4 shows that the use of selenium dioxide by itself decreased thecorrosion rate slightly to 40 mpy. The combination of seleniumdioxide+antimony bromide+propargyl alcohol resulted in a much lowercorrosion rate (11 mpy) than the combination of antimony bromide andpropargyl alcohol (30 mpy).

TABLE 4 Corrosion Rate SeO₂ SbBr₃ Propargyl Alcohol (mpy) (ppm) (ppm)(wt. %) 40.4 2500 — — 42.5 — — — 37.0 — 2500  — 41.9 — — 0.25 30.1 5000.2 11.1  250 250 0.2

EXAMPLE 5 Four Components-Mixture

Four components, chosen from selenium dioxide, morpholine, antimonybromide, propargyl alcohol, and isoascorbic acid, were tested. Thecorrosion rate results are summarized in Table 5 below.

TABLE 5 Propargyl Isoascorbic Corrosion SeO₂ Morpholine SbBr₃ Alcoholacid Rate (mpy) (ppm) (wt. %) (ppm) (wt. %) (wt. %) 8.7 100 0.2 150 —0.4 17.0 150 0.2 150 — 0.4 9.6 250 0.2 250 0.2 — 10.4 100 0.2 150 0.2 —6.9 100 0.2 150 0.2 — 17.2 50 0.15 120 0.2 — 19.4 50 0.15 120 0.2 — 15.350 0.15 120 0.2 — 35.0 50 0.15 45 0.2 —

The results for this set of tests may be summarized as follows:

Selenium dioxide+morpholine+antimony bromide+isoascorbic acid resultedin a corrosion rate of 9-17 mpy;

selenium dioxide+morpholine+antimony bromide+propargyl alcohol resultedin a corrosion rate decreasing from 35 mpy to 7 mpy, as amounts ofmorpholine and antimony bromide increased.

EXAMPLE 6 Five Components-Mixture

A five-component mixture consisting of selenium dioxide, morpholine,antimony bromide, propargyl alcohol, and isoascorbic acid was tested.Corrosion rates are summarized in Table 6, showing a low corrosion rateof 9.7 mpy, decreasing to a value as low as 3.5, when further adjustingmorpholine and isoascorbic acid.

TABLE 6 Propargyl Isoascorbic Corrosion SeO₂ Morpholine SbBr₃ Alcoholacid Rate (mpy) (ppm) (wt. %) (ppm) (wt. %) (wt. %) 9.7 100 0.2 150 0.20.15 3.5 100 0.15 150 0.2 0.4

EXAMPLE 7 Five Components-mixture, Introducing Hexamine

Hexamine was added to a four component mixture consisting of seleniumdioxide, morpholine, antimony bromide, and propargyl alcohol. Thecorrosion rate decreased from 10.4 mpy to 5.7 mpy.

TABLE 7 Propargyl Corrosion SeO₂ Morpholine SbBr₃ Alcohol Hexamine Rate(mpy) (ppm) (wt. %) (ppm) (wt. %) (ppm) 10.4 100 0.2 150 0.2 — 5.7 1000.2 150 0.2 150Summary

Summarizing the results obtained for the different combinations testedfor corrosion inhibition, the following conclusions may be drawn (thempy values relating to 350° F.):

Non-sulfur corrosion inhibitors for lowering the corrosion rate below 30mpy may contain, for example, a) antimony compound, and propargylalcohol; or b) antimony compound, propargyl alcohol, and morpholine; orc) antimony compound, propargyl alcohol, and isoascorbic acid.

The corrosion inhibitors for lowering the corrosion rate below 25 mpymay contain d) antimony compound, morpholine, and isoascorbic acid; e)antimony compound, propargyl alcohol, and selenium dioxide; or f)antimony compound, morpholine, selenium dioxide, and isoascorbic acid.

The corrosion inhibitors that can lower the corrosion rate below 10 mpymay contain g) antimony compound, propargyl alcohol, morpholine, andisoascorbic acid; or h) antimony compound, propargyl alcohol,morpholine, and selenium dioxide i) antimony compound, propargylalcohol, Morpholine, selenium dioxide, and isoascorbic acid; or j)antimony compound, propargyl alcohol, morpholine, selenium dioxide, andhexamine.

Table 8 shows the above conclusions about corrosion rates, denoting thepresence of a compound by ‘x’. SbX₃ may be SbCl₃ or SbBr₃.

TABLE 8 Corrosion Propargyl Rate (mpy) SbX₃ Alcohol MorpholineIsoascorbic acid SeO₂ Hexamine a <30 x x b <30 x x x c <30 x x x d <20 xx x e <20 x x x f <20 x x x x g <10 x x x x h <10 x x x x i <10 x x x xx j <10 x x x x x

Besides the above tested mixtures, aqueous salt mixtures with inhibitorsaccording to prior art recipes were prepared but they either did notproduce low corrosion rates or they showed disadvantageous features(such as undesired surface and interphase phenomena).

A skilled person will utilize the potential of the invention, which canprovide an anticorrosive composition for various situations, taking intoaccount the desired corrosion rate, phenomena other than corrosion,behavior of the inhibited brine, physical conditions during the intendeduse (temperature, pressure, additional chemical components from theenvironment, etc.), as well as other aspects, including economic,environmental, and safety aspects. For example, some specificapplications will require very low mpy values, other may necessitate lowcosts while doing with relatively higher mpy values, taking advantage offlexibility enabled by the invention. Said variety of practical aspectswill affect the selection of chemicals and their quantities effectedaccording to the invention by a skilled person.

While examples of the invention have been described for purposes ofillustration, it will be apparent that many modifications, variationsand adaptations can be carried out by persons skilled in the art,without exceeding the scope of the claims.

1. A liquid composition, in the form of a clear solution, comprising ahigh capacity aqueous carrier in which (i) 0.40-0.60% by weight of anantimony halide and (ii) morpholine or one or more4-(2-hydroxyalkyl)morpholine derivatives are dissolved, wherein thesolution further comprises (iii) 7-18% by weight straight chain primaryalkenol having from 3 to 5 carbon atoms and (iv) 20-30% by weight(iso)ascorbic acid wherein the water content of the composition is notless than 30% by weight.
 2. A composition according to claim 1, which isa clear solution containing about 30-60% by weight water.
 3. Acomposition according to claim 2, wherein the antimony halide is SbCl₃,the morpholine derivative is 4-(2-hydroxyethyl)morpholine and thealkenol is selected from group consisting of allyl alcohol(CH₂═CHCH₂OH), crotyl alcohol (CH₃CH═CHCH₂OH) and a mixture thereof.